This invention relates to an injectable composition comprising polymeric bodies, particularly deformable hydrogel macrodisks. The invention is also concerned with a process for preparing said composition and to a method for treating a tissue condition, particularly for tissue augmentation, by injecting said composition into the site of said condition.
The use of various injectable or inflatable polymeric bodies for tissue augmentation and prosthetic implants is known in the art. For example, U.S. Pat. No. 4,686,962 discloses an assembly for hypodermically implanting a genitourinary prosthesis for the treatment of urinary incontinence which includes an inflatable containment membrane which is inflated by material injected with a hypodermic needle.
Urinary incontinence also has been treated by the transurethral injection of polytetrafluoroethylene (PTFE), usually in the form of a paste or encapsulated particles. See, for example, "Transurethral Polytetrafluoroethylene Injection for Post-prostatectomy Urinary Incontinence" by M. Kaufman et al, the Journal of Urology, Vol. 132, September 1984, p. 463-464, and the references cited therein. However, if the particles are small, complications arise from undesirable migration or removal by phagocytes causing potential problematical accumulation at other sites, for example the brain, kidney or lungs.
Another application for tissue augmentation is in the treatment of a hypoplastic breast wherein a typical prior art prosthesis is provided by a silicone membrane enveloping a suitable bulking material, for example a saline solution or a flexible polysiloxane gel. One disadvantage of the saline-containing prosthesis is that microleaks in the silicone membrane or valving mechanism lead to deflation of the prosthesis. A problem with polysiloxane gel is that it contains low-molecular weight compounds, such as cyclic oligomers, which slowly migrate into the patient's system and cause problems similar to those associated with the PTFE particles discussed above.
A solution to the problems associated with earlier polymeric implants is provided by U.S. Pat. No. 4,631,188, which discloses a method of in situ formation of a solid polymer in a mammal which comprises injecting into said mammal a physiologically-acceptable polymeric composition comprising a solution in a water-soluble, non-toxic polar solvent of a water-insoluble, non-toxic, non-cross-linked polymer or copolymer selected from polymers and copolymers of acrylonitrile or vinylacetate, linear or slightly branched polymers and copolymers of 2-hydroxyethylacetate and methacrylate, poly-(N-vinyliminocarbonyl), polycondensates and polyadducts and having a solubility parameter of from about 9.2 to about 15.5 (cal/cc).sup.1/2.
The water-insoluble non-toxic polymers used in the method disclosed in U.S. Pat. No. 4,631,188 fall within the class of compounds known in the art as water-swellable hydrogels and the disclosure in said patent relating to this class of compounds is incorporated herein by reference. As noted in the patent, water-swellable hydrogels have been used in the art for tissue augmentation, usually in implants of defined shape and size. The method disclosed in the patent overcomes problems associated with such preformed implants by injecting a solution of said hydrogel into a mammal resulting in the in situ formation of a solid polymer in the mammal. This method involves the use of a water-soluble polar solvent, for example dimethyl sulfoxide (DMSO), which, although non-toxic, is an unnecessary adjunct to the implant and has to be dispersed by the mammal's metabolism. Furthermore, since the polymer is water-insoluble but water-swellable, formation of the solid polymer is dependent upon the amount of water present in the mammalian tissue and the size and shape of the implant is difficult to control.
Surprisingly, it has now been found that an injectable composition based upon a water-insoluble, non-toxic hydrogel but not containing undesirable solvents may be provided if the hydrogel is in the form of discrete, deformable bodies as hereinafter described. Moreover, the discrete, deformable bodies, since they already contain their full complement of water, retain their individual identity and are stable after injection so that the size and shape of the implant does not alter.